21-cm radiation is important because
it allows us to study neutral hydrogen in the interstellar medium
In the interstellar medium, molecules survive only in regions with
all of the above
Molecular clouds are best observed at ___________ wavelengths.
Interstellar clouds are
regions where hydrogen tends to be denser than the surrounding gas
“Weather” in the interstellar medium is produced
by supernovae and strong winds from luminous stars
Of the following forces at work in molecular clouds, which inevitably dominates the clouds’ evolution?
A young protostar is ___________ than the sun even though its surface temperature is ___________.
more luminous; cooler
What happens as a protostar contracts?
All of the above are true
The entire process of star formation is really just an evolving balance between
pressure and gravity
A cloud fragment too small to form a star becomes
a brown dwarf
The source of energy for a contracting protostar comes from
gravitational potential energy
A Hayashi track on an H-R diagram is a path of approximately constant
The most common types of stars in our galaxy are
Which of the following stars spend the longest time on their Hayashi tracks?
0.1 M₀ stars
A star’s evolutionary “track” in the H-R diagram traces out
how the star’s luminosity, temperature, and size change with time
A main sequence star is distinguished by
hydrogen burning in its core
The evolutionary cutoff between low- and high-mass stars occurs around
What factor is most important in determining a star’s position on the main sequence and subsequent evolution?
The main sequence lifetime of a star is given by the equation
t = M/L
As a main sequence star burns its core supply of hydrogen, what happens?
Helium builds up as ash in the core
The luminosity of a star depends on
how efficient its fuel is and how fast it burns
Hydrogen shell burning proceeds increasingly faster due to
heat released from the core’s contraction
The sun will likely stop being a main sequence star in
5 billion years
When a G2 star leaves the main sequence,
its luminosity increases and its surface temperature decreases
Degenerate refers to a state of
Just as a low-mass main sequence star runs out of fuel in its core, it actually becomes more luminous. How is this possible?
The outer layers expand due to the high rate of fusion in a shell around the dead core
When a star depletes its core supply of hydrogen, ___________ dominates in the core and ____________ dominates in the atmosphere.
A low-mass main sequence star’s climb up the red giant branch is halted by
the beginning of helium fusion in the core
When helium fusion begins in the core of the star, the situation quickly gets out of control because electron degeneracy pressure does not respond to changes in
A star’s surface temperature during the horizontal branch phase is determined primarily by its
Asymptotic giant branch (AGB) stars lose their atmosphere because
they have a low surface gravity
What is a planetary nebula?
The ejected envelope of a giant star surrounding a stellar core remnant
In a white dwarf, what is the source of pressure that halts its contraction as it cools?
Electrons packed so closely that they become incompressible
The gas in a planetary nebula comes from
hydrogen and elements processed in the core of the post-asymptotic giant branch star
One star in a binary will almost always become a red giant before the other because
small differences in main sequence masses yield large differences in main sequence ages
A nova is the result of which explosive situtation?
Mass transfer onto a white dwarf
A Type I supernova occurs when a white dwarf exceeds a mass of ____________.
A Cepheid star varies in luminosity because
only the outer envelope of the star pulsates
Hawking radiation exists from black holes because
space itself has physical properties
At about what mass do we distinguish between high-mass and low-mass stars?
The more efficient CNO cycle of hydrogen fusion can take place in high-mass stars because of the greater ___________ in their cores.
What prevents the buildup of a core of helium ash in a high-mass main sequence star?
Mixing by convection
As a high-mass main sequence star evolves off the main sequence, it follows a ___________ the HR diagram.
roughly horizontal path
When pulsating variable stars are at their brightest, they are also
largest and bluest
The main difference between Cepheid variable stars and RR Lyrae stars is
If you measure the pulsation period of a Cepheid variable star, you can also determine its
An iron core cannot support a star because
iron cannot fuse with other nuclei to produce energy
Why does the luminosity of a high-mass star remain nearly constant as the star burns heavy elements in its core, even though it is producing millions of times more energy per second than it did on the main sequence?
The energy is carried off in the form of neutrinos
The collapse of the core of a high-mass star at the end of its life takes about
Essentially all the heaviest elements in the galaxy are formed during
a supernova explosion
A neutron star contains the mass of up to three Suns in a sphere with a diameter approximately the size of
Which of the following does not describe a neutron star?
All of these describe a neutron star
What characteristic of a star cluster is used to determine its age?
The main sequence turnoff point
X-ray binaries result from a process similar to that in a
What would happen if mass were continually added to a 2.0 solar mass neutron star?
The star would eventually become a black hole
Light is increasingly redshifted near a black hole because
time is moving increasing ly slower in the observer’s frame of reference
The event horizon of a black hole is defined as
the radius at which the escape speed equals the speed of light
If the Sun were to be replaced by a one solar mass black hole, the gravitational pull of the black hole “sun” on Earth would be
An indestructible robot would feel ____________ as it crossed the event horizon of a black hole
Black holes are best studied in the ____________ band of radiation.
What do astronomers mean when they say that the universe is homogeneous?
Stars and galaxies are generally distributed similarly throughout the universe
The spectra of most galaxies tell us that
most galaxies appear to be moving away from us
According to Hubble’s Law, as the distance of a galaxy ____________; its _____________ increases.
increases; recessional velocity
Hubble’s constant H₀ represents
the rate of expansion of the universe
Astronomers use galactic redshift as a measure of
If suddenly we find that the distance between Earth and the Sun is not 10 percent larger than we thought it was before, what will change?
All of the above
If we lived on a galaxy one billion light-years from our own, what would we see?
Much the same universe we see today
If you lived today on the farthest quasar we can see and looked around, what would you see?
A universe much as we see it today
Galaxies move away from us in all directions because
space is expanding
Where in the universe did the Big Bang take place?
Everywhere in the universe
Assuming a Hubble time of 13.6 billion years and a constant rate of expansion, what was the scale factor (R₀) of the universe 10.2 billion years ago (compared to today)?
At a redshift of z = 1,000, the universe was
1000 times smaller than it is today
The temperature of the cosmic background radiation 2.73 K corresponds to a peak wavelength of around
If, at the time of recombination, the wavelength of the background radiation peaked at 1 um, how old was the universe, compared to today?
1/1,000th as old
Which of the following elements was not created as a result of Big Bang nucleosynthesis?
Why does the overall mass of the universe decide its ultimate fate?
The greater the mass of the universe, the more gravitationally bound the universe will be.
If the fate of the universe were determined solely by the total mass of the universe (luminous and dark), astronomers would predict that we live in a universe that will
stop expanding and eventually copllapse
How does the addition of a nonzero cosmological constant affect the expansion of the universe?
It is possible for the density of the universe to be above the critical mass density and still expand forever
The fact that we live in an accelerating universe indicates that the age of the universe is ____________ the Hubble time.
The inverse of the value of H₀ is
In a spherical universe, the sum of the angles in a triangle sum to
more than 180°
Why is the fact that the cosmic background radiation (CBR) is near smooth considered a problem?
A universe as smooth as predicted by the CBR should never have occurred because quantum mechanics states that the universe had to have started with fluctuations too great to have smoothed out
Protostars are difficult to observe because
a. the protostar stage is very short.
b. they are surrounded by cocoons of gas and dust.
c. they radiate mainly in the infrared.
Interstellar gas clouds may collapse to form stars if they
encounter a shock wave.
____ are small luminous nebulae excited by nearby young stars.
a measure of the resistance to the flow of radiation (photons) through a gas.
The visual pink glow of the Great Nebula in Orion
is an emission nebula of thin gas.
The ____ is the nuclear fusion of three helium nuclei to form a carbon nucleus.
Emission nebulae are also called ____ because they are composed of ionized hydrogen.
____ are star-like objects that contain less than 0.08 solar masses and will never raise their core temperatures high enough that the proton-proton chain can begin. Other minor fusion reactions do occur in these objects. They fall in a gap between the low-mass M dwarf stars and the massive planets in which nuclear fusion never occurs.
The average star spends ____ of its lifetime on the main sequence.
The lower edge of the Main Sequence band is known as ____ and represents the location in the H-R diagram at which stars begin their lives as main sequence stars.
the zero-age main sequence
____ is the thermonuclear fusion of hydrogen to form helium operating in the cores of massive stars on the main sequence.
The CNO cycle
The diagram below is an H-R diagram. The line indicates the location of the main sequence. Which of the five labeled locations on the HR diagram indicates a luminosity and temperature similar to that of a T Tauri star?
In the proton-proton chain
energy is produced in the form of gamma rays and the velocity of the created nuclei.
The carbon-nitrogen-oxygen cycle
combines four hydrogen nuclei to form one helium nucleus, which produces energy.
What causes the outward gas pressure that balances the inward pull of gravity in a main sequence star?
c. the high temperature of the gas
d. the high density of the gas
The free-fall contraction of a molecular cloud
can be initiated by shock waves from supernovae.
Convection is important in stars because it
b. mixes the gases of the star.
c. transports energy outward in the star.
____ occurs when most of the material collapsing to form a protostar has fallen into a disk around the star, and a strong wind from the warm protostar ejects material from its poles.
A bipolar outflow
Which of the following is NOT evidence of the existence of an interstellar medium?
molecular absorption lines in the spectra of cool stars
Molecular clouds can be observed
using radio telescopes to observe the CO emission from the clouds.
The H-R diagram main sequence of stars has a limit at the lower mass, or energy output end, because
there is a minimum temperature for hydrogen nuclear fusion (the definition of a star).
There is a main sequence mass-luminosity relation because
more massive stars support their larger weight by making more energy.
Due to the dust in the interstellar medium, a distant star will appear to an observer on Earth to be
fainter and cooler than it really is.
The lowest mass object that can initiate thermonuclear fusion of hydrogen has a mass of about
0.08 solar masses.
Stars with masses less than ____ produce most of their energy via the proton-proton chain.
1.1 solar masses
The creation of ____ require(s) that a young hot star (T 25,000 K) be relatively nearby.
The extinction of starlight due to the interstellar medium
I. is the greatest in the ultraviolet.
IV. is caused by dust particles.
____ are small dark nebulae about 1 light-year in diameter that contain 10 to 1,000 solar masses.
Absorption lines due to the interstellar medium indicate that some components of the interstellar medium are cold and of a very low density because
the lines are extremely narrow.
Stars are born in
dense molecular clouds.
Absorption lines due to interstellar gas
are more narrow than the lines from stars because the gas has a lower pressure than stars.
What is the lifetime of a 10 solar mass star on the main sequence?
What is the lifetime on the main sequence of a 2 solar mass star compared to the approximately 10 billion year life of our Sun? Pick the best answer.
If the dust around a protostar radiates most strongly at 30 microns or 30,000 nm, what is the approximate temperature of that dust? Hint: T in K =3,000,000/wavelength in nm.
A jet has an angular length of 10 seconds of arc and flows from a star at a distance of 2,000 pc. How far does this jet extend away from the star?
The H-R diagram of a young star cluster shows
that low mass stars have not yet reached the main sequence yet.
As a star begins to form, the initial energy source is from
gravitational potential energy.
While on the main sequence a star’s primary energy source comes from
What must occur for an object to be considered a main sequence star?
a. Hydrostatic equilibrium
b. Nuclear fusion reaction in the core
What force(s) are responsible for the collapse of an interstellar cloud?
Star clusters are important to the study the stellar evolution because stars in a given cluster have the same
Why do higher mass stars live shorter lives on the main sequence than lower mass stars?
Higher mass stars burn through their nuclear fuel faster.
Why do nuclear fusion reactions only take place in the interior of a star?
b. The temperature is the hottest in the center.
c. The density of material is very high in the center.
What characteristic of a star primarily determines its location on the main sequence?
Parallax would be easier to measure if
Earth’s orbit was larger.
Absolute visual magnitude is
the apparent magnitude of a star observed from a distance of 10 pc.
A star’s luminosity depends only on the star’s
temperature and diameter.
In an H-R Diagram, stars with the smallest radius are found in the ____ of the diagram.
lower left corner
In the H-R diagram, 90 percent of all stars are
on the main sequence.
We know that giant stars are larger in diameter than the sun because
they are more luminous but have about the same temperature.
Red giant stars are
I. more luminous than the sun.
II. larger in diameter than the sun.
III. cooler than B stars.
IV. located above the main sequence stars in the H-R diagram.
Compared with the spectral lines in the solar spectrum, lines in a supergiant star’s spectrum are
The most common stars are
lower (less luminous) main sequence stars.
The ____ of a star is a measure of the total energy radiated by the star in one second.
To determine the orbital period of a visual binary, we must measure
position on the sky.
In a binary system, the more massive star
is nearest the center of mass.
The total mass of the pair of stars in spectroscopic binaries are difficult to estimate because
we can’t see the shape or tilt of the orbit.
Which star in Diagram 13-1 is most like the sun?
Which star in Diagram 13-1 has the greatest surface temperature?
Which of the stars in Diagram 13-1 has the largest absolute visual magnitude?
An eclipsing binary will
also be observed as a spectroscopic binary.
If we can solve the orbital motion of an eclipsing binary, we can find
a. the mass of each star.
b. the diameter of each star.
Which of the following kinds of stars best obey the mass-luminosity relation?
main sequence stars
Which of the following kinds of stars is most dense?
a white dwarf
A spectroscopic binary shows periodic variations in its
Stars on the main sequence with the greatest mass
are spectral type O stars.
The total mass of a binary system can be calculated from
the semi major axis and period of the orbit.
The diagram below illustrates two stars in a visual binary system and the center of mass of this system. Based on this diagram, what is the ratio of the mass of star A to the mass of star B?
1 to 2
If a star has a parallax of 0.02 seconds of arc, then its distance is
If a star with an absolute magnitude of −5 has an apparent magnitude of +5, then its distance is
An eclipsing binary has been analyzed and it has been determined that the ratio of the mass of star A to the mass of star B is 6 and the total mass of the two stars is 26 solar masses. What are the masses of star A and star B?
Star A has a mass of 22.3 solar mass and star B has a mass of 3.7 solar masses.
What is the total mass of a binary star system with P = 20 yr and a = 10 AU?
2.5 solar masses
At what point in the light curve below is the cooler star in front of the hotter star?
36. From the data given, which star in Table 13-1 would appear the faintest in the night sky?
37. From the data given,, which star in Table 13-1 has the greatest luminosity?
38. From the data given,, which star in Table 13-1 is the closest to Earth?
39. From the data given,, which star in Table 13-1 has the greatest surface temperature?
40. From the data given,, which star in Table 13-1 has the greatest diameter?
41. Which star in Table 13-2 is the closest to Earth?
42. Which star in Table 13-2 has the greatest surface temperature?
43. Which star in Table 13-2 has the greatest diameter?
If two stars are emitting the same amount of light, the star that is farther will appear
We can determine the surface temperature of a star from
a. studying its continuous spectrum.
b. studying its line absorption spectrum.
c. measuring the star’s luminosity.
Which stars always have large positive absolute magnitude?
Stars of low luminosity.
How can we tell that some stars are relatively close to us in the sky?
Some stars appear to move periodically back and forth against the background stars because of the Earth’s movement around the Sun.
The most accurate way to determine the surface temperature of a star is to study
the pattern of absorption lines from various atoms.
If you compare two stars,
the one with the smaller absolute magnitude will always have the greater luminosity.
Stars in the upper right part of the Hertzsprung-Russell diagram are always ____ when compared to stars near the middle of the diagram.
How is a luminosity class assigned to a star?
By studying the absorption line width in the spectrum of the star.
As a main sequence star exhausts hydrogen in its core, its surface becomes ___ and its energy output per second (luminosity) becomes ____.
As a main sequence star exhausts hydrogen in its core, it next becomes
a red giant star.
A star will experience a helium flash if
a. it is less massive than about 3 solar masses.
b. its has become a red giant star.
c. its has formed a helium core.
d. the material in the core has gradually become degenerate.
In degenerate matter
pressure does not depend on temperature.
Giant and supergiant stars are rare because
the giant or supergiant stage is very short.
A(n) ____ is a collection of 100 to 1000 stars in a region about 25 pc in diameter. The stars in the collection are typically quite young.
A(n) ____ is a collection of 105 to 106 stars in a region 10 to 30 pc in diameter. The stars in the collection tend to be more than 109 years old and mostly yellow and red stars.
Stars within a cluster that are at the turnoff point
have life expectancies that are equal to the age of the cluster.
In star clusters, the ____ stars are giant stars fusing helium in their cores and then in their shells.
In the orbital plane of a binary star system, matter can be transferred from one star to the other at the ________ located directly between the two stars is the point where the Roche lobes meet.
A mass is transferred in a normal star in a binary system toward a white dwarf, the material forms a rapidly growing whirlpool of material known as a(n)
____ is a form of electromagnetic radiation produced by rapidly moving electrons spiraling through magnetic fields.
The Crab nebula is
Star clusters are important to our study of stars because
they give us a method to test the our theories and models of stellar evolution.
What is the approximate age of the star cluster in the H-R diagram below? Hint: Main sequence stars of spectral types between A and B core’s supply of hydrogen is sufficient to last about 250 million years. Between A and F about 2 billion years. Type G about 10 billion years. Between K and M about 30 billion years.
10 billion years
The triple alpha process
occurs during helium flash.
Which of the following nuclear fuels does a one-solar mass star use over the course of its entire evolution?
hydrogen and helium
Helium flash occurs
because degenerate electrons in the core do not allow the core to expand as it heats up.
Stars in a star cluster
a. all have the same age.
b. all have the same chemical composition.
If the stars at the turnoff point of a cluster have a mass of 3 M, what is the age of the cluster?
In the diagram below, which point indicates the location on the H-R diagram of a one solar mass star when it undergoes helium flash?
The lowest-mass stars cannot become giants because
they cannot heat their centers hot enough.
A planetary nebula is
the expelled outer envelope of a medium mass star.
The Chandrasekhar limit tells us that
white dwarfs more massive than 1.4 solar masses are not stable.
A Type I supernova is believed to occur when
a white dwarf exceeds the Chandrasekhar limit.
Massive stars cannot generate energy through iron fusion because
both fusion or fission of iron nuclei absorb energy.
The theory that the collapse of a massive star’s iron core produces neutrinos was supported by
the detection of neutrinos from the supernova of 1987.
Synchrotron radiation is produced by
high-velocity electrons moving through a magnetic field.
A nova is almost always associated with
a white dwarf in a close binary system.
The Algol paradox is explained by considering
mass transfer between the two stars in a binary system.
Stars with masses between 0.4 and 4
undergo thermonuclear fusion of hydrogen and helium but never get hot enough to ignite carbon.
A type-II supernova
c. is characterized by a spectrum that shows hydrogen lines.
d. occurs when the iron core of a massive star collapses.
Synchrotron radiation is produced
in supernova remnants.
When material expanding away from a star in a binary system reaches the Roche surface
the material is no longer gravitationally bound to the star.
A white dwarf is composed of
carbon and oxygen nuclei and degenerate electrons.
A planetary nebula
produces an emission spectrum.
If the theory that novae occur in close binary systems is correct, then novae should
repeat after some interval.
As a white dwarf cools its radius will not change because
pressure does not depend on temperature for a white dwarf because the electrons are degenerate.
The diagram below shows a light curve from a supernova. How many days after maximum light did it take for the supernova to decrease in brightness by a factor of 100?
A planetary nebula has a radius of 0.5 pc and is expanding at 20 km/sec. What is the approximate age of this planetary nebula? (1 pc is equal to 3×1013 km, and 1 year is equal to 3.15×107 seconds.)
About how long will a 0.5 star spend on the main sequence?
57 billion years
For a star of Sun-like mass, what is the last stage of the nuclear fusion?
helium to carbon and oxygen
What are the two longest stages in the life of a one solar mass star?
main sequence, white dwarf
What nuclear fusion mechanism does an isolated white dwarf use to generate energy?
White dwarfs don’t generate their own energy.
Stars that have ejected a planetary nebula eventually become
After what evolutionary stage does a star become a white dwarf?
Where are elements heavier than iron primarily produced?
The explosion of a supernova typically leaves behind
a shell of hot, expanding gas with a pulsar at the center.